This invention relates to closed nozzle fuel injectors having a control chamber for permitting servo-control of a needle valve element and, specifically, to a servo-controlled closed nozzle injector which effectively control needle valve movement to enhance injector operation and combustion in an engine.
In most fuel supply systems applicable to internal combustion engines, fuel injectors are used to direct fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for resisting blow back of exhaust gas into the pumping or metering chamber of the injector while allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring to block fuel flow through the nozzle orifices. In many fuel systems, when the pressure of the fuel within the nozzle cavity exceeds the biasing force of the nozzle spring, the nozzle valve element moves outwardly to allow fuel to pass through the nozzle orifices, thus marking the beginning of injection. In another type of system, such as disclosed in U.S. Pat. No. 5,676,114 to Tarr et al., the beginning of injection is controlled by a servo-controlled needle valve element. The assembly includes a control volume positioned adjacent an outer end of the needle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve. U.S. Pat. No. 5,463,996 issued to Maley et al. discloses a similar servo-controlled needle valve injector.
Internal combustion engine designers have increasingly come to realize that substantially improved fuel supply systems are required in order to meet the ever increasing governmental and regulatory requirements of emissions abatement and increased fuel economy. It is well known that the level of emissions generated by the diesel fuel combustion process can be reduced by decreasing the volume of fuel injected during the initial stage of an injection event and decreasing the time required for valve closing. It is also desirable to limit the impact velocity of the needle valve element against its seat upon closing. As a result, many proposals have been made to provide control devices in closed nozzle fuel injector systems. U.S. Pat. No. 5,133,645 to Crowley et al. discloses a common rail fuel injection system having two common rails serving respective banks of injectors. Fuel is supplied to each rail by a respective cam-operated reciprocating plunger pump. Each injector includes a nozzle element positioned in a spring cavity which receives high pressure fuel from the common rail via a check valve. The spring cavity is also connected, via an orifice, to a pressure control volume positioned above the nozzle element. A solenoid operated control valve opens to connect the control volume to drain thereby initiating injection as fuel flows from the nozzle cavity through the orifice to drain, and closes to terminate injection. U.S. Pat. No. 4,249,497 to Eheim et al. discloses a fuel injection system wherein fuel injection is controlled by controlling the differential pressure across a nozzle valve element using a single valve which opens to direct fuel to drain so as to start injection and closes to end injection. However, these references fail to disclose a means for effectively controlling the rate of needle valve element opening and closing.
U.S. Pat. No. 5,638,791 to Tsuzuki et al. and U.S. Pat. No. 5,771,865 to Ishida both disclose a common-rail fuel injection system with a fuel injector having a back pressure control chamber (pressure chamber) which is fluidically connected to a high-pressure inlet port (fuel pipe) and a control port (low pressure passage) which drains to a solenoid actuator. These references also disclose orifices that restrict the flow of fluid into the back pressure control chamber and the solenoid actuator passage.
U.S. Pat. No. 5,941,215 to Augustin is noted for disclosing a fuel injector having a spring chamber which is fluidically connected to a supply line via a passage which acts as a simple throttle structure.
U.S. Pat. No. 2,959,360 to Nichols discloses a fuel injector nozzle assembly incorporating passages in the nozzle assembly for diverting the fuel from the nozzle assembly. Specifically, Nichols discloses a nozzle valve element having an axial passage formed therein for diverting fuel from the nozzle cavity into an expansible chamber formed in the nozzle valve element. A plunger is positioned in the chamber to form a differential surface creating a fuel pressure induced seating force on the nozzle valve element to aid in rapidly seating the valve element. The Nichols reference does not suggest the desirability of controlling the rate of opening and closing of the nozzle valve element.
Although some systems discussed hereinabove control needle valve element movement, further improvement is desirable. None of the above discussed references disclose a fuel injector incorporating a simple servo-controlled needle valve capable of increasing the time required to open the needle valve element and decreasing the time required for valve closing while limiting the impact velocity of the needle valve element against its seat upon closing.
It is an object of the present invention, therefore, to overcome the disadvantages of the prior art and to provide a fuel injector which is capable of effectively and predictably controlling the opening and closing of a needle valve element to permit control of the rate of fuel injection.
It is another object of the present invention to provide a servo-controlled injector capable of effectively slowing the opening of the needle valve element.
Yet another object of the present invention is to provide a servo-controlled injector capable of effectively speeding up the closing of the needle valve element.
It is another object of the present invention to provide a servo-controlled injector capable preventing the needle valve element from sticking in the open position.
It is yet another object of the present invention to provide a servo-controlled injector permitting the flow rate of fuel injected during the initial portion of the injection event to be more accurately controlled so as to minimize emissions.
It is a further object of the present invention to provide an injector for use in a variety of fuel systems, including common rail system, accumulator pump systems and pump-line-nozzle fuel systems, which effectively controls the rate of injection.
It is a still further object of the present invention to provide a servo-controlled injector capable of preventing needle valve element bounce in the open position.
Still another object of the present invention is to provide a servo-controlled injector wherein the needle valve element can hover on a fuel cushion when in the open position.
Yet another object of the present invention is to provide an injector which offers maximum flexibility in controlling injection rate shape.
Still another object of the present invention is to provide a servo-controlled injector which provides a quick needle valve element closing while limiting the impact velocity of the needle valve element against its seat.
It is a still further object of the present invention to provide a servo-controlled injector capable of minimizing parasitic fuel losses.
These and other objects of the present invention are achieved by providing a closed nozzle injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body containing an injector cavity and an injector orifice communicating with one end of the injector cavity to discharge fuel into the combustion chamber wherein the injector body includes a fuel transfer circuit for transferring supply fuel to the injector orifice. The injector also includes a nozzle valve element positioned in one end of the injector cavity adjacent the injector orifice and movable between an open position in which fuel may flow from the fuel transfer circuit through the injector orifice into the combustion chamber and a closed position in which fuel flow through the injector orifice is blocked. Movement of the nozzle valve element from the closed position to the open position and from the open position to the closed position defines an injection event during which fuel may flow through the injector orifice into the combustion chamber. The needle valve element includes an inner guide portion having an outer surface contacting the injector body and an outer guide portion having an outer surface contacting the injector body. The inner guide outer surface includes an outer diameter greater than an outer diameter of the outer guide outer surface. The closed nozzle injector further includes an outer control volume positioned adjacent an outer end of the needle valve element, a control volume charge circuit for supplying fuel from the fuel transfer circuit to the outer control volume, a drain circuit for draining fuel from the outer control volume to a low pressure drain, an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit to control the movement of the needle valve element between the open and closed positions and an inner control volume positioned axially along the needle valve element between the inner guide portion and the injector orifice.
The closed nozzle injector may include a spring chamber positioned axially along the needle valve element between the inner guide portion and the outer guide portion and a bias spring positioned in the spring chamber to bias the needle valve element toward the closed position. The spring chamber is positioned to receive unrestricted high pressure fuel from the fuel pressure circuit. The fuel injector may further include an inner restriction orifice positioned to restrict fuel flow from the fuel transfer circuit to the inner control volume wherein the inner restriction orifice is sized to create a pressure difference between the fuel transfer circuit and the inner control volume. The fuel injector may further include an outer restriction orifice positioned to restrict fuel flow from the fuel transfer circuit to the outer control volume. The outer diameter of the inner guide outer surface is sized to generate a fuel pressure biasing force acting on the inner guide portion which tends to bias the needle valve element toward the closed position during an injection event. The needle valve element may be a one-piece unitary structure including the inner and the outer guide portions. The needle valve element may further include a valve seat portion have a valve seat diameter less than the outer guide portion diameter. The inner restriction orifice may be formed in the needle valve element.
The present invention is also directed to a closed nozzle injector for injecting fuel at a high pressure into the combustion chamber of an engine comprising the injector body, the nozzle valve element movable between open and closed positions, the outer control volume, the control volume charge circuit, the drain circuit, the injection control valve and a needle valve biasing feature for creating a fuel pressure bias closing force on the needle valve element which biases the needle valve element toward the closed position and for increasing the fuel pressure bias closing force on the needle valve element during movement from the closed position to the open position. The needle valve biasing feature further functions for creating a fuel pressure bias opening force on the needle valve element which biases the needle valve element toward the open position and for increasing the fuel pressure bias opening force as the needle valve element moves from the open position toward the closed position. The needle valve biasing feature may further include the inner guide and outer guide portions, the inner control volume, the inner restriction orifice, the outer restriction orifice and/or the valve seat portion having a valve seat diameter less than the outer guide portion diameter.